Acoustic diaphragm



7, 1965 M. F. NOREN ETAL 3,221,334

ACOUSTIC DIAPHRAGM Filed May 9, 1963 FIGI 2 INVENTORS! MAURITZ F. NOREN RICHARD H. SCENT ATT'YS United States Patent 3,221,834 ACOUSTIC DIAPHRAGM Mauritz F. Noren and Richard H. Scent, St. Charles, Ill., a'ssiguors to Hawle y Products Company, St. Charles, 11]., a corporation of Delaware Filed May 9, 1*)63, Ser. No. 279,233 3 (Zlai'rns. (Cl. 181-32) This invention relates to an acoustic diaphragm and more particularly to an acoustic diaphragm for dynamic loudspeakers.

One of the objects of the invention is to provide an acoustic diaphragm with a built in cutoff factor whereby the higher range frequencies are cut off fairly sharply.

Another object of the invention is to provide an acoustic diaphragm of the type described having improved strength.

Still a further object of the invention is to provide a relatively shallow acoustic diaphragm which is exceptionally strong.

A further object of the invention is to provide an acoustic diaphragm which has a relatively wide response for a given height.

Still a further object of the invention is to provide a relatively light weight acoustic diaphragm which can be made in the form of a relatively shallow structure, which does not break readily under normal operating conditions and which provides better power handling.

A more specific object of the invention is to provide a new and improved elliptical acoustic diaphragm.

Other objects and advantages of the invention will appear from the following description in conjunction with the accompanying drawings in which FIGURE 1 is a plan view illustrating an embodiment of the invention in the form of an elliptical acoustic diaphragm adapted for use in a dynamic loudspeaker;

FIGURE 2 is a cross sectional view taken along the line 22 of FIGURE 1;

FIGURE 3 is a modification of the cross sectional view shown in FIGURE 2 illustrating the positioning of ribs in the surface of the diaphragm; and

FIGURE 4 is a partial plan view illustrating the appearance of the ribbed diaphragm shown by the cross sectional view of FIGURE 3.

In accordance with the invention an acoustic diaphragm is provided having a vibratile portion, a supporting flange portion and an interconnected undulating portion, said vibratile portion extending upwardly and inwardly from said undulating portion to a tubular nipple, said vibratile portion having a reverse curvature and being convex in the lower portion adjacent said undulating portion and concave in the upper portion adjacent said nipple, the point of change of curvature from convex to concave being approximately the midpoint of said vibratile portion.

In the embodiment of the invention shown in the drawing, the vibratile portion is ellipsoidal and the flange portion and the undulating portion are elliptical.

For the purpose of the invention the walls of the vibratile portion can be smooth as shown in FIGURES 1 and 2 but it is desirable to form at least one rib adjacent the point of change of curvature and preferably at least one rib on each side of the point of change of curvature of the vibratile portion. The point of change of curvature acts as a pivot point and the provision of one or more ribs serves to reinforce the vibratile portion adjacent this point. The use of these ribs also makes it possible to mold the vibratile portion from thinner material. In the embodiment shown in FIGURES 3 and 4 it will be noted that there is one reinforcing rib on the upper side of the point of curvature and a plurality of reinforcing ribs in the convex area of the vibratile portion.

The acoustic diaphragm shown in FIGURE 1 comprises a supporting flange portion 1, an undulating portion 2, and a vibratile portion 3 which extends upwardly and generally inwardly from the undulating portion to a tubular nipple 4.

From FIGURE 2 it will be seen that the vibratile portion has a convex area 5 and a concave area 6 on the long axis which gradually merges with a'convex area 7 and a concave area 8 on the short axis. The base of the tubular nipple 4 where it intersects the vibratile portion 3 is herein referred to as the shoulder of the diaphragm. The height of the diaphragm is the vertical distance from the shoulder 9 to the base line 10. While the invention is not limited to use on shallow diaphragms, its use is especially advantageous in making such diaphragms.

The point of change of curvature is indicated at 11. At this point the convex curvature changes to a concave curvature. This is approximately, although not necessarily, exactly at the midpoint of a straight line drawn from the shoulder 9 to the point 12 of the base 10.

The construction of the undulating portion 2 is subject to some variation. Thus in a typical 6" x 9" elliptical acoustic diaphragm made in accordance with the invention the groove 13 would have a radius of 0.063"; the groove 14 would have a radius of 0.039"; the groove 15 would have a radius of 0.063"; the groove 16 would have a radius of 0.039" and the groove 17 would have a radius of 0.078".

The material employed in constructing the diaphragm is preferably a felted fibrous cellulosic material and the diaphragm is preferably formed by accreting cellulose fibers from an aqueous slurry onto a porous former. This method of manufacture is conventional in making acoustic diaphragms and is not a part of the present invention. It is ordinarily customary to mold the diaphragm with a cap or top 18 which is severed at 19 so that the tubular portion 4 can receive a voice coil of a loudspeaker.

The flange 1 which is normally employed to hold the diaphragm in a loudspeaker can, if desired, coincide with the base line 10.

In the embodiment shown in FIGURE 3 the point of change of curvature is indicated by the numeral 20. The structure of the flange 1 and the undulating portion 2 is each essentially the same as that previously described with respect to FIGURES l and 2. The vibratile portion 3 differs, however, in that it is provided with a series of ribs 21, 22, 23, 24, 25, 26 and 27. The rib 21 is on the upper side of the point 20 and the other ribs are on the lower side. There are no ribs in the area 28 adjacent the shoulder 29. It will also be noted that the spacing between the ribs is at a minimum on the short axis and increases to a maximum on the long axis. In a typi cal 6 x 9" elliptical diaphragm of the type shown in FIGURES 3 and 4 a suitable spacing is about Ms" on the short axis and A" on the long axis. Stated in another way, the total overall space occupied by the ribs on the short axis is about 1 and the total overall space occupied by the ribs on the long axis is about 1%". By using this type of structure in a molded cellulose fiber diaphragm it is possible to decrease the average thickness to about 0.010" to 0.013" whereas without the ribs the thickness of the vibratile portion would be on the order of 0.020" to 0.030. In the embodiment shown in FIG- URES 3 and 4, the ribs are constructed in the form of undulations whereby the interior of the diaphragm contains a series of grooves opposite the ribs. This struc' ture is subject to variation and it will be understood that the ribs can be constructed in such a way that these grooves are filled in so as to give a smooth surface on the interior of the diaphragm.

The invention is not limited to the use of any particular material in constructing the diaphragm. While it is preferable to employ the felted cellulose fiber material, other materials, such as resinous or plastic materials capable of being molded, can be employed. Such materials, of course, must have a suitable amount of flexibility or resilience to provide the vibration necessary to transmit sound.

In the diaphragm shown in the drawings the angle formed by a straight line connecting the shoulder 9 with the base 10 at the point 12 is relatively small, preferably about 16. The diameter of the tubular portion 4 is usually about 1" but this is subject to variation. In the particular diaphragm shown, the height is about 0.855. Thus, this diaphragm is very shallow. The invention is particularly advantageous in making diaphragms having a height of less than about 2" but is applicable to the manufacture of all sizes of diaphragms.

One of the main advantages of the invention is the provision of an acoustic diaphragm which affords a relatively sharp cutoff of sounds in the higher frequency range. Another advantage of the invention is the provision of an acoustic diaphragm which affords better power handling, greater efliciency and wider response for the same height and with a smaller weight. In the embodiment of the invention employing body ribs it is possible to reduce the weight from an average of say 3 grams to about 2.25 to 2.50 grams for a 6" x 9" elliptical diaphragm. The gradually increased spacing between the ribs from the short axis to the long axis affords greater resistance to breakup. Since breakup increases in shallow diaphragms, the invention, including the rib structure, is especially useful in such diaphragms.

The invention is hereby claimed as follows:

1. An acoustic diaphragm having an ellipsoidal vibratile portion, an elliptical supporting flange portion and an interconnected elliptical undulating portion, said vibratile portion extending upwardly and inwardly from said undulating portion to a tubular nipple, said vibratile portion having a reverse curvature, being convex in the lower portion adjacent said undulating portion and concave in the upper portion adjacent said nipple, the point of change of curvature being approximately the midpoint of said vibratile portion and there being a rib of elliptical shape on each side of said point of change of curvature.

2. An acoustic diaphragm as claimed in claim 1 in which the spacing between said ribs varies, being at a minimum on the short axis and gradually increasing to a maximum on the long axis of the vibratile portion.

3. An acoustic diaphragm having a vibratile portion, a supporting flange portion and an interconnected undulating portion, said vibratile portion extending upwardly and inwardly from said undulating portion to a tubular nipple, said vibratile portion having a reverse curvature and being convex in the lower portion adjacent said undulating portion and concave in the upper portion adjacent said nipple, the point of change of curvature from convex to concave being approximately the midpoint of said vibratile portion, said acoustic diaphragm having at least one rib above and at least one rib below said point of change of curvature.

References Cited by the Examiner UNITED STATES PATENTS 1,807,225 5/1931 Pack 181-32 1,872,081 8/1932 Hawley 181-32 2,890,760 6/1959 Bobb 1s1 -32 FOREIGN PATENTS 562,932 9/1923 France.

928,176 5/1947 France.

399,182 7/1924 Germany.

LEO SMILOW, Primary Examiner. 

1. AN ACOUSTIC DIAPHRAGM HAVING AN ELLIPSOIDAL VIBRATILE PORTION, AN ELLIPTICAL SUPPORTING FLANGE PORTION AND AN INTERCONNECTED ELLIPTICAL UNDULATING PORTION, SAID VIBRATILE PORTION EXTENDING UPWARDLY AND INWARDLY FROM SAID UNDULATING PORTION TO A TUBULAR NIPPLE, SAID VIBRATILE PORTION HAVING A REVERSE CURVATURE, BEING CONVEX IN THE LOWER PORTION ADJACENT SAID UNDULATING PORTION AND CONCAVE IN THE UPPER PORTION ADJACENT SAID NIPPLE, THE POINT OF CHANGE OF CURVATURE BEING APPROXIMATELY THE MIDPOINT OF SAID VIBRATILE PORTION AND THERE BEING A RIB OF ELLIPTICAL SHAPE ON EACH SIDE OF SAID POINT OF CHANGE OF CURVATURE. 